Metal flakes of copper or aluminum composition of submicron thickness and multimicron lateral face dimensions are recognized to be a potential source for an infrared screening cloud for military purposes. The metal powder is packed in a camouflage system such as a canister, missile, rocket or a gas generator and dispersed in the atmosphere. The cloud or aerosol that is formed camouflages and/or screens point targets on fortresses, air parts etc., especially against attacking precisely guided weapons.
Thus, U.S. Pat. No. 4,100,102 (Shaffer) describes a composition for use in generating a protective aerosol, consisting essentially of a suspension of 30-40 wt. % aluminum particles in 60-70 wt. % of vaporizable hydrocarbon oil, the aluminum particles having diameters in the range 2-20 microns and thicknesses of &lt;0.3 micron. The specification of this patent makes clear that these "particles" are in fact flakes, which are commercially available for use as a pigment. In an example, the mass extinction coefficient of these aluminum flakes, termed in this patent the "J-value", is shown to lie within the range 2.3-2.5 m.sup.2 /g in respect of infrared radiation.
Moreover, U.S. Pat. No. 3,975,292 (Shaffer) describes a method for forming a protective aerosol, wherein a suspension of aluminum particles in a hydrocarbon oil are fed into a hot, high velocity gas stream, the temperature of which is sufficiently high to vaporize the oil, the mixed stream of hot gases, hydrocarbon oil and aluminum particles (having diameters in the range 2-20 microns and thicknesses of &lt;0.3 micron) being discharged into the atmosphere. U.S. Pat. No. 4,484,195 (Shaffer) describes a method of screening infrared radiation using an aerosol of aluminum particles having essentially dimensions of the same order of magnitude as the wavelengths of such radiation.
The use of aluminum is also featured in U.S. Pat. No. 4,286,498 (Block et al), wherein there is described a method for producing burst charges for dispersing energy generating material in an effective pattern for confusing energy sensing devices (operating on infrared, sonar or microwave reflected energy) wherein KClO.sub.4 (5 pbw) which has passed through a #20 screen is mixed with black aluminum (2 pbw), screening the mixture through a #20 screen a predetermined no. of times, and placing a fusing member therein.
The use of copper composition flakes is featured for example in U.S. Pat. No. 4,704,966 (Sellman et al), which describes a method of screening against visual and infrared light by injecting into the atmosphere a cloud of fine metal flakes of submicron thickness and multimicron lateral face dimensions and comprised of a copper composition, the cloud being formed by bursting a compacted cohesive solid mass of the metal flakes in the atmosphere, thereby forming a dispersed aerosol.
Furthermore, U.S. Pat. No. 4,704,967 (Milstead et al) describes a product for screening against visual and infrared light, made by slurrying fine metal flakes of submicron thickness and multimicron lateral face dimensions and in particular comprised of a copper composition, with a volatile liquid to wet the flakes, which adhere to one another in compacted form at the bottom of the slurry, the liquid being removed to leave a mutually face-to-face compact adhered solid mass of metal flakes. In practice, the compacted slurry is extruded and the wet extrusions are cut into small segments and removal of the liquid is effected by evaporative drying.
The use of additives admixed with the metal powder or flakes is featured e.g. in U.S. Pat. No. 4,622,899 (Weber), which describes a smoke generating projectile containing both optical smoke powder and infrared absorbing powder, besides igniter compositions. The infrared absorbing powder may be copper, preferably in lamellar form of 3200-16000 cm.sup.2 /g surface area and 1.9-0.45 micron diameter, possibly mixed with a dispersion agent such as ammonium phosphate, polytetrafluoroethylene or highly dispersed SiO.sub.2. Also, U.S. Pat. No. 5,233,927 (Wulvik) describes a smoke camouflage system including metallic (e.g. brass) powder, and a cold-flow properties improving material such as aluminum silicate or a sand-blowing material.
The entire contents of each of the above-mentioned U.S. Patents is explicitly incorporated herein by reference.